1. Field of the Invention
This invention relates to offshore platforms used for drilling operations. More particularly, it relates to tension leg platforms used in conjunction with another vessel in tender-assisted drilling operations.
2. Description of the Related Art including information disclosed under 37 CFR 1.97 and 1.98.
Both tension leg platforms (TLP's) and semi-submersible floating vessels (“semis”) can be used for offshore drilling and production operations.
It can be difficult and costly to provide a TLP with adequate space for all the drilling and completion equipment needed to drill and complete a well—e.g., drill pipe, drilling and completion risers, casings, other tubular goods and drilling and completion fluids. Tenders are often employed to provide the required space needed on a rig and/or platform during the initial drilling and completion phase of an offshore oilfield. However, a problem exists in that most tenders cannot be kept alongside a platform in a constant spaced-apart relationship during extreme weather so as to colliding with the platform. Specifically, tenders have not been able to remain in a connected capacity and avoid the risk of collision.
U.S. Pat. No. 6,619,223 to Beato and entitled “Tender with hawser lines” describes a hawser system for connecting a semisubmersible tender to a deep draft caisson vessel comprising: a first winch and a second winch disposed on the first end of the tender; a first hawser connected to the first winch and a second hawser connected to the second winch; a first sheave and a second sheave disposed on a second end of the tender opposite the first end of the tender, the first sheave for engaging the first hawser and the second sheave for engaging the second hawser; a first hawser fairlead disposed on a first side of the tender for receiving the first hawser and a second hawser fairlead disposed on the second side of the tender for receiving the second hawser and wherein the first hawser crosses the second hawser three times as each is reaved to each fairlead and wherein the first and second hawsers pass beneath the deck of the tender to the deep draft caisson vessel; at least one connector or joining the first and second hawsers at a position in the deep draft caisson vessel, after the hawsers pass each fairlead.
U.S. Pat. No. 6,575,111 also to Beato and entitled “Method for tendering” describes a method of using a semi-submersible tender with a deck, a shape that results in a combined environmental load less than 1000 kips in a 100-year extreme weather condition, a plurality of supports each with a rounded shape connected to the deck, a plurality of pontoons connecting the supports with each pontoon being capable of ballast transfer, wherein the tender is used for mooring in a tendering position relative to an offshore platform using hawsers with adequate elasticity to accommodate the wave frequency between the platform and the tender and adequate stiffness to synchronize the mean/low frequency movement between the platform and the tender under an environmental load produced during a 10-year winter storm, and enough slack during a 10-year storm to enable the tender to move to a tender standby position, and wherein the tender uses an at least 6-point mooring system for creating global equilibrium between the platform and the tender.